The invention pertains to the treatment of wastewater to remove pollutants. More specifically, the invention provides method for the biological treatment of wastewater for the oxidation of carbonaceous pollutants, usually expressed as BOD.sub.5 and the physical removal of particulate matter. The method of the present invention employs rotating partially submerged biological contactors to grow aerobic biological slimes for the oxidation of carbonaceous matter and a settling zone subjacent to the contactors for removal of particulate matter from the biologically treated wastewater.
BOD.sub.5 is a measure of the concentration of biodegradable organic carbon in a medium obtained by determining the amount of oxygen consumed (mg/l) by the medium at 68.degree. F in 5 days. The term filtrate BOD.sub.5 is used to define the amount of soluble and colloidal carbonaceous matter present in wastewater after filtration of all particles larger than about 0.5 micron. The expression filtrate BOD.sub.5 loading rate is used herein to express the amount of filtrate BOD.sub.5 supplied per day per 1,000 square feet of contactor surface i.e. (lbs/day/1,000 sq.ft.). All percentages are by weight unless otherwise specified.
U.S. Pat. No. 3,575,849 issued to Torpey discloses a method and apparatus for biologically treating wastewater including a treatment tank having a biological treatment zone in its upper portion and a quiesent settling zone in its lower portion. The biological treatment zone includes a plurality of parallel rotatable shafts disposed across the upper portion of the tank; each of the shafts supporting a plurality of biological contactors, typically thin discs. The contactors extend into the wastewater in the tank to less than half the tank depth, providing a subjacent settling zone for sloughed off solids. The surface of the biological contactors is alternately exposed to the atmosphere and wastewater at suitable intervals to promote the growth of aerobic biological slimes.
The Torpey U.S. Pat. No. 3,776,841 discloses a wastewater treatment tank having an upper biological treatment zone including rotating partially submerged contactors to grow aerobic biological slimes and a subjacent settling zone. The subjacent settling zone is physically separated from the biological treatment zone by a false bottom or longitudinal baffle. Wastewater is introduced into the upper biological treatment zone, flows through the upper zone, around the longitudinal baffle and into and through the subjacent settling zone to a treated wastewater outlet.
The Torpey et al U.S. Pat. No. 3,849,304 discloses a treatment tank including a plurality of adjacent upper biological treatment bays employing rotating contactors and a plurality of lower subjacent settling zones. The upper biological treatment zones and the lower settling zones are separated by a horizontal baffle extending across the tank. Raw wastewater enters the lower settling zone of one of the bays wherein solids are removed, and is then vertically directed into and through the upper biological treatment zone of the first bay. From the first bay the wastewater is horizontally directed into and through the biological treatment zone of the second bay and is subsequently vertically directed into and through the lower settling zone of the second bay. Preferably, two secondary bays, each receiving about one half of the wastewater flow from the first bay, are provided.
Pending application Ser. No. 523,704 now U.S. Pat. No. 3,932,273 by Torpey et al. discloses a method utilizing a composite apparatus for the treatment of wastewater to remove settleable and floatable solids and to remove and oxidize organic matter including a treatment tank having at least two horizontally adjacent bays, each of the bays having an upper biological treatment zone separated by a horizontally disposed baffle from a lower settling zone. Raw wastewater enters the lower settling zone of one of the bays wherein settleable and floatable solids are removed, and then turns vertically to flow in a reverse direction through the upper biological treatment zone of each bay. From the upper treatment zones the wastewater is directed into and through the lower settling zone of the second bay from which the treated fluid is removed.
The U.S. Pat. No. 3,563,383 to Hellquist, pertains to a complete method for treating organically polluted wastewater including biological treatment using partially submerged contactors in the upper portion of a section of the treatment unit. The Hellquist system utilizes a plurality of separate bays arranged in series for primary settling before the wastewater enters the biological treatment section.